Resin tube

ABSTRACT

A resin tube has a high impact resistance unparalleled by conventional resin tubes formed of a material containing polyamide 11 resin or polyamide 12 resin as a principal component. The resin tube has a plurality of resin layers including at least one impact-resistant resin layer formed of a composite material prepared by mixing 65 to 75 parts by weight polyamide 11 resin as a first material (A) and 25 to 35 parts by weight composite polyamide 11 resin prepared by adding a proper amount of an olefin elastomer to polyamide 11 resin as a second material (B).

TECHNICAL FIELD

The present invention relates to a resin tube to be used as a fuel lineon an automobile and, more particularly, to a resin tube having animproved impact resistance.

BACKGROUND ART

Metal tubes coated with a plated film or a resin film have beengenerally used as fuel lines on automobiles. The corrosion resistanceand chemical resistance of metal tubes have been enhanced through theimprovement of coating materials and the construction of coating films.

Recently, resin tubes have been prevalently used as fuel lines as wellas metal tubes. Resin tubes have many advantages; resin tubes arerustproof while metal tubes are subject to rusting, are easy to process,increase the degree of freedom of design and are lightweight.

Thermoplastic resins prevalently used for forming resin tubes as fuellines of this kind include polyamide 11 resin and polyamide 12 resin.Polyamide 11 resin and polyamide 12 resin are excellent in chemicalresistance and heat resistance and are suitable materials for formingtubes for fuel lines.

On the other hand, tubes formed of materials containing polyamide 11resin as a principal component and those containing polyamide 12 resinas a principal component have low flexibility. In some cases, thosetubes are difficult to arrange in forming piping. A plasticizer is addedto a material for forming resin tubes to make the resin tubes flexible.

In view of safety, resin tubes for fuel lines are required to have highimpact resistance such that the resin tubes will not crack when animpulsive force is exerted thereon to prevent fuel leakage.

High-performance laminated tubes have been developed in recent years.Each of those laminated tubes consists of layers of different resins.For example, a laminated tube having an improved fuel permeationinhibiting ability has layers respectively formed of a polyphenylenesulfide resin (PPS resin), an ethylene-vinyl alcohol resin (EvOH resin),a polybutylene naphthalate resin (PBN resin) and a liquid crystallizedpolymer (LCP). A laminated tube proposed in JP 2002-338173 A by theapplicant of the present invention patent application is one of suchlaminated tubes.

Although the conventional resin tubes formed of a material containingpolyamide 11 resin or polyamide 12 resin as a principal component, and aplasticizer have flexibility owing to the effect of the plasticizer, theplasticizer is unable to improve the cold impact resistance of the resintubes.

When an impact is made on a laminated tube including resin layers havinglow impact resistance, cracks are developed in the resin layers havinglow impact resistance and the cracks propagate over the entire laminatedtube.

DISCLOSURE OF THE INVENTION

Accordingly, it is an object of the present invention to solve thoseproblems in the prior art and to provide a resin tube having a highimpact-resistant ability unparalleled by the conventional resin tubesformed of a material containing polyamide 11 resin or polyamide 12 resinas a principal component.

Another object of the present invention is to provide a laminated tubehaving a sufficient impact-resistant ability even if the laminated tubeincludes a resin layer susceptible to impacts.

A laminated resin tube in a first aspect of the present inventionincludes a plurality of resin layers of thermoplastic resins; wherein atleast one of the plurality of resin layers is an impact-resistant resinlayer formed of a composite material prepared by mixing 65 to 75 partsby weight polyamide 11 resin as a first material (A) and 25 to 35 partsby weight composite polyamide 11 resin prepared by adding a properamount of an olefin elastomer to polyamide 11 resin as a second material(B).

A representative polyamide resin as the polyamide 11 resin of the firstmaterial (A) is a polyamide resin having acid amide bonds or acopolymerized amide resin containing a polyamide resin having acid amidebonds and can be produced by polymerizing 11-amino undecanoic acid.

The composite polyamide 11 resin as the second material (B) is anelastomer containing olefin as a principal component. Preferable olefinis, for example, ethylene, propylene and butylenes. The olefin elastomercontent of the second material (B) is 5 to 10% of 100 parts by weight ofthe composite polyamide 11 resin. A commercially available compositepolyamide 11 resin of the second material (B) is, for example, RilusanF15XN (Atofina Japan).

Quantities of pellets of the polyamide 11 resin of the first material(A) and those of the composite polyamide resin of the second material(B) corresponding to the contents are mixed by a mixer, and the mixedpellets are plasticized by an extruder. The laminated tube is formed bya coextrusion process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a resin tube in a first embodimentaccording to the present invention;

FIG. 2 is a cross-sectional view of a resin tube in a second embodimentaccording to the present invention;

FIG. 3 is a cross-sectional view of a resin tube in a third embodimentaccording to the present invention;

FIG. 4 is a cross-sectional view of a resin tube in a fourth embodimentaccording to the present invention;

FIG. 5 is a cross-sectional view of a resin tube in a modification ofthe resin tube in the fourth embodiment; and

FIG. 6 is a table showing results of cold impact tests of examples ofthe present invention and comparative examples.

BEST MODE FOR CARRYING OUT THE INVENTION

Resin tubes embodying the present invention will be described withreference to the accompanying drawings.

First Embodiment

FIG. 1 shows a resin tube in a first embodiment according to the presentinvention in a cross-sectional view. This resin tube is a three-layertube having a first layer, namely, the innermost layer to be exposed tofuel, a second layer, namely, an adhesive layer, and a third layer,namely, the outermost layer. The third layer is an impact-resistantresin layer formed of a composite material prepared by mixing 65 to 75parts by weight polyamide 11 resin as a first material (A) and 25 to 35parts by weight composite polyamide 11 resin as a second material (B)prepared by adding a proper amount of an olefin elastomer to polyamide11 resin.

The first layer may be formed of a thermoplastic resin suitable forforming a resin tube for a fuel line. To provide a resin tube having ahigh fuel permeation inhibiting ability, the first layer is formed by alow-permeability resin having a low permeability to fuel, such as one ofpolyphenylene sulfide resins (PPS resins), polybutylene naphthalateresins (PBN resins), liquid crystallized polymers (LCPs), ethylene-vinylalcohol resins (EvOH resins), ethylene tetrafluoroethylene resins (ETFEresins) and polyvinylidene fluoride resins (PVDF resins).

Second Embodiment

FIG. 2 shows a resin tube in a second embodiment according to thepresent invention in a cross-sectional view. This resin tube is afour-layer tube having a low-permeability first layer, namely, theinnermost layer, a low-permeability second layer, a third layer, namely,an adhesive layer, and an impact-resistant fourth layer, namely, theoutermost layer.

The first layer is formed of conductive composite resin prepared bymixing carbon fibers in a PPS resin. The second layer is formed of anonconductive PPS resin not containing carbon fibers. Thus the first andthe second layer form a double-wall, conductive, low-permeabilitystructure having high fuel permeation inhibiting ability and capable ofdischarging static electricity. The PPS resin has satisfactorily lowpermeability and insufficient impact resistance. The high impactresistance of the impact-resistant fourth layer compensates for theinsufficient impact resistance of the PPS resin forming the first andthe second layer.

Although the first and the second layer are formed of the samelow-permeability resin in the second embodiment, the first and thesecond layer may be formed of different low-permeability resins,respectively. For example, when the first layer is formed of a LCPhaving a low permeability to all kinds of fuels and the second layer isformed of an EVOH resin having a low permeability to regular gasoline,the combined effect of the first and the second layer exercise highpermeation inhibiting ability regardless of the type of the fuel.

Third Embodiment

FIG. 3 shows a resin tube in a third embodiment according to the presentinvention in a cross-sectional view. This resin tube is a five-layerresin tube having a first layer, namely, the innermost layer, formed ofan ordinary resin not having particularly low permeability, alow-permeability second layer, a low-permeability third layer, anadhesive fourth layer and an impact-resistant fifth layer, namely, theoutermost layer.

Fourth Embodiment

FIG. 4 shows a resin tube in a fourth embodiment according to thepresent invention in a cross-sectional view. This resin tube is asix-layer resin tube having a low-permeability first layer, alow-permeability second layer, an adhesive third layer, alow-permeability fourth layer, an adhesive fifth layer and animpact-resistant sixth layer. The low-permeability first, second andfourth layers and the adhesive third layer form a three-layerlow-permeability structure. The six-layer resin tube has high permeationinhibiting ability and the impact-resistant sixth layer protects thelow-permeability layers not sufficiently resistant to impact.

FIG. 5 shows a six-layer resin tube in a modification of the resin tubein the fourth embodiment in a cross-sectional view. This resin tube hasa conductive first layer, an impact-resistant second layer, an adhesivethird layer, a low-permeability fourth layer, an adhesive fifth layerand an impact-resistant sixth layer, namely, the outermost layer. Thusthe low-permeability fourth layer is held between the impact-resistantsecond and sixth layers, and the impact-resistant second layer protectsthe conductive first layer. When the fourth layer is formed of alow-permeability resin having poor impact resistance, the constructionof this resin tube is effective in preventing the propagation of cracksdeveloped in the fourth layer across the other layers.

Although the laminated resin tubes according to the present inventionhave been described by way of example, the present invention isapplicable to a single-layer resin tube formed on an impact-resistantresin.

EXAMPLES

A resin tube in an example of the resin tube in the first embodiment andresin tubes in comparative examples were subjected to cold impact tests.FIG. 6 shows the results of the cold impact tests. The third layersrespectively having different thicknesses of the examples and thecomparative examples were formed of composite materials prepared bymixing the first material (A) according to the present invention,namely, the polyamide 11 resin, and the second material (B) according tothe present invention, namely, the composite polyamide 11 resin preparedby adding a proper amount of an olefin elastomer to polyamide 11 resinin different weight ratios, respectively.

Each of the resin tubes in the example and the comparative example had afirst layer of a PPS resin having a thickness of 0.2 mm and an adhesivesecond layer having a thickness of 0.1 mm.

The outermost layer of the resin tube in Comparative example 1 wasformed of polyamide 11 resin containing a plasticizer (BESN BK OTL,Atofina Japan). The outermost layer of the resin tube in Comparativeexample 2 was formed of polyamide 11 resin containing a plasticizer(BESN BK P20TL, Atofina Japan). The outermost layer of the resin tube inComparative example 3 was formed of the second material (B), namely, thecomposite polyamide 11 resin prepared by adding a proper amount of anolefin elastomer to polyamide 11 resin (Rilusan F15XN, Atofina Japan).The outermost layers of the resin tubes in Comparative examples 4 and 5were formed of composite materials prepared by mixing the secondmaterial (B) in the first material (A) in increased weight ratios.

In the cold impact tests, a weight 450 g and a weight of 300 g weredropped from a height of 300 mm onto the test resin tube after keepingthe test resin tube in an atmosphere of −40° C for 5 hr. The test resintubes were examined visually for cracks. In FIG. 6, circles indicate thetest resin tubes in which cracks were not developed and crosses indicatethe test resin tubes in which some cracks were developed.

As apparent from FIG. 6, the resin tube in Comparative example 1 havingthe outermost layer formed of the polyamide 11 resin not containing anyplasticizer have low impact resistance. It is known from data on theresin tube in Comparative example 3 that the second material (B),namely, the composite polyamide 11 resin, is not an impact-resistantresin.

The resin tube in Example having the outermost layer formed of thecomposite resin containing the second material (B), namely, thecomposite polyamide 11 resin, in 25 to 35% by weigh has an exceedinglyhigh impact resistance. The resin tube in Comparative example 5 havingthe outermost layer formed of the composite material containing thecomposite polyamide 11 resin in an excessively high weight ratio has alow impact resistance. The resin tube in Comparative example 4 and theresin tube in Comparative example 2 having the outermost layer formed ofpolyamide 11 resin containing a conventional plasticizer are equivalentin impact resistance.

It is expected that the thinner the impact-resistant layer, the lower isthe impact resistance of the impact resistance. The results of impacttests prove this fact. However, it is not necessarily true that animpact-resistant layer having a greater thickness is desirable. Adesirable thickness of the impact-resistant layer is in the range of 0.7to 0.9 mm.

As apparent from the foregoing description, according to the presentinvention, the resin tube is formed of the materials containing thepolyamide 11 resin as a base component has a high impact-resistingability unparalleled by the conventional resin tubes formed of materialscontaining polyamide 11 resin or polyamide 12 resin as a principalcomponent.

According to the present invention, the resin tube including theimpact-resistant layer and the low-permeability layer having low impactresistance in combination prevents the development of cracks in thelow-permeability layer and has a sufficiently high impact resistance.

1. A laminated resin tube comprising a plurality of resin layers ofthermoplastic resins; wherein at least one of the plurality of resinlayers is an impact-resistant resin layer formed of a composite materialprepared by mixing 65 to 75 parts by weight pellets of polyamide 11resin as a first material (A) and 25 to 35 parts by weight pellets ofcomposite polyamide 11 resin prepared by adding a proper amount of anolefin elastomer to polyamide 11 resin as a second material (B).
 2. Theresin tube according to claim 1, wherein the outermost resin layer isthe impact-resistant layer of a thickness in the range of 0.7 to 0.9 mm.3. The resin tube according to claim 1, wherein at least either of anintermediate resin layer and the innermost resin layer is alow-permeability resin layer.
 4. A resin tube according to claim 3,wherein the innermost resin layer is a first low-permeability resinlayer formed of a conductive polyphenylene sulfide resin (PPS resin), aresin layer enclosing the innermost layer is a second low-permeabilityresin layer formed of a nonconductive polyphenylene sulfide resin (PPSresin), and the outermost layer is the impact-resistant resin layer. 5.A resin tube formed of a composite resin containing 65 to 75 parts byweight polyamide 11 resin as a first material (A) and a compositepolyamide 11 resin prepared by adding a proper amount of an olefinelastomer to polyamide 11 resin as a second material (B).
 6. A method ofmanufacturing a laminated tube having a plurality of resin layers ofthermoplastic resins, said method comprising the steps of: producing 65to 75 parts by weight pellets of polyamide 11 resin as a first material(A); producing 25 to 35 parts by weight pellets of composite polyamide11 resin prepared by adding a proper amount of an olefin elastomer topolyamide 11 resin as a second material (B); producing a composite resinby mixing the respective pellets of the polyamide 11 resin and thecomposite polyamide 11 resin; and forming a laminated resin tubeincluding at least one impact-resistant resin layer of the compositeresin.